For the time before records began, we have only "proxy records" reconstructed largely from tree rings and ice cores, supplemented by a few incomplete written accounts.
在开始有记录之前，我们只有主要根据年轮和冰芯重建的“代理记录”，还有一些不完整的书面记录作为补充。
Studies of tree rings and ice cores indicate a more recent cycle of seven years, still much less frequent than the present cycle of every three or four years.
树的年轮、冰轮的研究证明了后来厄尔尼诺现象以七年为周期的，仍然比现在的每三年或四年发生一次的频率要低得多。
Estimates of earlier temperatures made from data such as ice cores and tree rings, though not as reliable as thermometers, suggest the decade may have been the warmest in the past millennium.
早期的气温数据是根据冰芯和树木年轮估算出来的，虽然不如温度计那么准确，但我们依然可看到，过去的十年是一千年来气温最高的十年。
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